Feed injection system for catalytic cracking process

ABSTRACT

A fluid catalytic cracking unit includes a nozzle located in the bottom of a riser reactor. A first conduit provides a passageway for enabling a dispersing gas to flow therethrough and through an outlet passageway in a cap covering the end of the conduit. The outlet passageway discharges the dispersing gas into a liquid hydrocarbon feed material flowing through a second conduit spaced from and enclosing the first conduit to form an annulus therebetween, thereby providing a passageway for enabling the liquid hydrocarbon feed material to flow. A second cap covers the end of the second conduit and is spaced from the first cap thereby forming a mixing zone therebetween for mixing the liquid hydrocarbon feed and the dispersing gas. The second cap includes a continuous circular slot as an outlet passageway of the first cap and is adapted for discharging the mixture of liquid hydrocarbon feed and the dispersing gas. Hot regenerated catalyst enters the riser bottom region through a regenerator standpipe.

This application is a 371 of PCT/EP00/08653 filed Sep. 1, 2000, which isa continuation-in-part of Ser. No. 09/390,230 filed Sep. 3, 1999, nowU.S. Pat. No. 6,387,247.

The present invention relates to feed injection systems and, inparticular, to feed nozzles used for catalytic cracking processes.

In a typical Fluid Catalytic Cracking Unit (FCCU) consisting of aregenerator, a riser reactor and a stripper, such as that shown in U.S.Pat. No. 5,562,818 to Hedrick which is incorporated herein by reference,finely divided regenerated catalyst is drawn from the regeneratorthrough the regenerator standpipe and contacts with a hydrocarbonfeedstock in a lower portion of a reactor riser. Hydrocarbon feedstockand steam enter the riser through feed nozzles. The mixture of feed,steam and regenerated catalyst, which has a temperature of from about200° C. to about 700° C., passes up through the riser reactor,converting the feed into lighter products while a coke layer deposits onthe surface of the catalyst. The hydrocarbon vapors and catalyst fromthe top of the riser are then passed through cyclones to separate spentcatalyst from the hydrocarbon vapor product stream. The spent catalystenters the stripper where steam is introduced to remove hydrocarbonproducts from the catalyst. The spent catalyst containing coke thenpasses through a stripper standpipe to enter the regenerator where, inthe presence of air and at a temperature of from about 620° C. to about760° C., combustion of the coke layer produces regenerated catalyst andflue gas. The flue gas is separated from entrained catalyst in the upperregion of the regenerator by cyclones and the regenerated catalyst isreturned to the regenerator fluidized bed. The regenerated catalyst isthen drawn from the regenerator fluidized bed through the regeneratorstandpipe and, in repetition of the previously mentioned cycle, contactsthe feedstock in the lower riser.

The most critical element of the FCCU riser reactor design is the feedinjection system. For peak performance, it is essential that the feedinjection system distributes the feed in fine spray having a uniformcoverage across the riser and a narrow droplet size distribution. Such aspray increases the surface area of the feed droplets and facilitatesintimate contacting with the regenerated catalyst. Existing feedinjection systems of prior art, however, have difficulty in achievingthis desired performance.

A typical FCCU can have either side entry nozzles or bottom entrynozzles to introduce the hydrocarbon feed into the riser reactor. Bottomentry nozzles introduce the hydrocarbon feed from the bottom of theriser reactor whereas side entry nozzles introduce the feed from theperiphery of the riser reactor and at a higher elevation. Most modernCCUs are designed with side entry nozzles. For FCCUs with side entryconfiguration, regenerated catalyst is transported upwards from thebottom of the riser by fluidizing gas, usually steam, and thehydrocarbon feed is injected by multiple nozzles mounted on theperiphery of the riser reactor at a higher elevation. Modern side entrynozzles, such as disclosed in U.S. Pat. No. 5,794,857 are, in general,good feed atomizers. However, the side entry configuration has severalsignificant drawbacks. The higher feed injection point leads to lowerriser reactor volume and lower catalyst circulation, due to higherpressure drop in the riser. The contact of hot, regenerated catalystwith transport steam at the lower riser also leads to higher catalystdeactivation before feed contacting.

Catalytic cracking units with bottom entry nozzles can avoid thedrawbacks of the side entry configuration described above. However,prior art bottom entry nozzles are, in general, not as good in feedatomization. U.S. Pat. No. 4,097,243 disclosed a bottom entry nozzledesign with multiple tips to distribute feed into multiple streams. Feedatomization was rather poor. In addition, feed was injected in asubstantially longitudinal direction of the riser which leads to slowmixing between the feed and the regenerated catalyst because both aremoving in a substantially parallel direction. This leads to anundesirable condition of feed contacting with a broad feed vaporizationzone in the reactor riser. A number of improvements, such asCA-A-1015004, U.S. Pat. No. 4,808,383, U.S. Pat. No. 5,017,343, U.S.Pat. No. 5,108,583, and EP-A-151882 disclose various means to improvefeed atomization for bottom entry nozzles. However, feed atomizationremains inadequate, and the feed injection remains substantiallylongitudinal, leading to slow mixing with regenerator catalyst andundesirable feed contacting in a broad vaporization zone.

U.S. Pat. No. 4,784,328 and EP-A-147664 disclose two complicated designsof mixing boxes at the bottom of the FCCU reactor riser to improvemixing between feed and regenerated catalyst. However, these mixingboxes have a very complicated geometry with many passages which make itdifficult to retain their mechanical integrity and proper functions overtime because the lower riser region is extremely erosive.

U.S. Pat. No. 4,795,547 and U.S. Pat. No. 5,562,818 disclose two bottomentry nozzles with different designs of diverter cones at the exit of asubstantially longitudinal feed pipe carrying atomized feed. Thefunction of these diverter cones is to redirect the substantiallyaxially flowing feed stream to a somewhat radially discharging feed atthe exit, thus intended for enhancing the mixing with the regeneratedcatalyst. However, there are major drawbacks in these diverter designs.First, the hydrocarbon feed is atomized upstream of the diverter andwhen the atomized feed impinges on the surface of the diverter cone atthe exit, re-coalescence of many of the atomized feed droplets occurs,leading to the formation of sheets of liquid discharging from the cone.The diverter cone achieves a change in the direction of the feed butthis comes at the high price of significantly worsening feedatomization. Second, the radially discharging feed in the form of liquidsheets from the diverter cone can penetrate through catalyst in theriser without much vaporization and impinges on the riser wall, leadingto major mechanical damage.

The object of the present invention is to provide an improved bottomentry feed injection system for use in catalytic cracking processeswhich will result in better feed distribution in the reactor riser.

This object is achieved with the following nozzle for use in a fluidcatalytic cracking unit comprising:

a first conduit for providing a passageway for enabling a firstdispersing gas to flow therethrough;

a first cap covering the end of said first conduit, said first capincluding at least one outlet passageway therethrough adapted fordischarging said first dispersing gas into a liquid hydrocarbon feedmaterial;

a second conduit enclosing said first conduit and spaced therefrom toform an annulus therebetween thereby providing a passageway for enablingsaid liquid hydrocarbon feed material to flow therethrough;

a second cap covering the end of said second conduit, said second capbeing spaced from said first cap thereby forming a mixing zonetherebetween for mixing said liquid hydrocarbon feed and said firstdispersing gas said and said second cap including at least one circularslot as outlet passageway therethrough, which passageway issubstantially aligned with the outlet passageway on said first cap andis adapted for discharging said mixture of said liquid hydrocarbon feedand said first dispersing gas, and

wherein a third conduit is present surrounding said second conduit andforming an annulus therebetween for providing a passageway for enablinga second dispersing gas to flow therethrough.

The present invention improves feed atomization of bottom entryinjection systems, thus eliminating the need for a side entryconfiguration and its drawbacks. It has been found that the bottom entryfeed injection system of the instant invention achieves an improved feedatomization and distribution achieving a uniform feed distributionacross the riser. The present feed injection system will distribute thehydrocarbon feed in a fine spray having a uniform coverage across theriser and a narrow droplet size distribution. Another advantage is thatthe atomized feed can be discharged in a substantially radial directionfor better mixing with regenerated catalyst, without having to use adiverter cone. A further advantage is that the atomized feed can bedischarged in a substantially radial direction, while not impinging theriser wall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a preferred embodiment of a FCCU with a single bottom entryfeed injection system.

FIGS. 2A/2B/2C show detail design features of the preferred feedinjection system of FIG. 1.

FIG. 3 shows a prior art single bottom entry feed injection system.

FIG. 4A shows a plan view of feed distribution in the riser of prior artside entry feed nozzles.

FIG. 4B shows a plan view of improved feed distribution provided by asingle nozzle according to the present invention.

FIGS. 5A/5B show detail design features of an even more preferred feedinjection system of FIGS. 2A/2B/2C.

FIGS. 6 and 7 show detail design features of another preferred feedinjection system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1 which shows a preferred embodiment of thepresent invention, a catalytic cracker riser reactor 1 is connected to aregenerator standpipe 2 through which hot, regenerated catalyst 3 entersthe riser bottom region. A liquid hydrocarbon feed 8, such as gas oil,and dispersing gas 4 and 12, such as steam, are introduced through asingle bottom entry nozzle assembly 100.

Preferably the nozzle is provided with a third conduit, as shown in FIG.1 as conduit 5. The third conduit surrounds the second conduit 38 andforms an annulus 6 therebetween for providing a passageway for enablinga second dispersing gas to flow therethrough.

Nozzle assembly 100 comprises three concentrically and substantiallyvertically arranged conduits. A first conduit 22 provides a passagewayfor a first dispersing gas 12 and terminates in a first cap 32. Firstconduit 22 and first cap 32 are surrounded by a second conduit 38terminating in a second cap 48, the annulus 9 formed thereby providing apassageway for liquid hydrocarbon feed 8. Second conduit 38 is, in turn,surrounded by a third conduit 5 which is open at the top. The externalsurface of conduit 5 is protected by an erosion resistant material 7,such as refractory or other material known to those skilled in the art,to prevent damage to the nozzle assembly 100 by the incoming hot,regenerator catalyst 3. The external surface of the second cap 48,extending beyond the termination of conduit 5 and into riser reactor 1,is protected by erosion resistant material, such as STELLITE 6 (STELLITEis a trade mark) or other material known to those skilled in the art. Afirst annulus 6 is formed between conduit 5 and conduit 38. A secondannulus 9 is formed between conduit 38 and conduit 22. Centering lugs 10in the first annulus 6 keep conduit 38 centered within conduit 5.Centering lugs 13 in the second annulus 9 keep conduit 22 centeredwithin conduit 38.

A first dispersing gas 12 enters first conduit 22 which terminates witha first cap 32 having at least one outlet passage 14 discharging ingenerally a radially outward and, preferably upward, direction intomixing zone 42, located in the vicinity of the discharge of outletpassage 14 between first cap 32 and second cap 48. Liquid hydrocarbonfeed 8 enters conduit 28, continues through substantially verticalsecond conduit 38 via annulus 9 to a second cap 48 and is mixed in across-flow with the first dispersing gas 12 in mixing zone 42, resultingin the formation of a fine two-phase mixture of small dispersed bubblesin heavy petroleum hydrocarbon liquid. Second cap 48 has at least onecircular slot outlet passage 11 for emitting the mixture of hydrocarbonfeed and first dispersing gas into the riser reactor 1 in a radiallyoutward and, preferably upward, direction. Passage 11 is substantiallyaligned with the discharge of the first dispersing gas 12 from outletpassage 14. As the fine two-phase mixture of small dispersed bubbles inheavy petroleum hydrocarbon passes through outlet passage 11 into riserreactor 1 to contact with regenerator catalyst 3, the two-phase mixturesuddenly expands, forming a hollow cone fine of atomization of heavypetroleum hydrocarbon feed with narrow droplet size evenly distributedacross the riser reactor 1.

Conduit 5 penetrates through the riser bottom 30 into riser 1 andterminates at a level 15 preferably above the center line 2 a ofregenerator standpipe 2. A second dispersing gas 4 passes throughconduit 24, and is directed into conduit 5 via the first annulus 6 andexits through the top of conduit 5 into the riser reactor 1 in asubstantially longitudinal direction. The second dispersing gas 4 hasseveral functions. One is to shield hot, regenerated catalyst 3 fromdamaging the feed injection nozzle 100 inside conduit 5 under normaloperation. Another function is to provide emergency fluidization gas fortransporting catalyst in case of feed outage.

Additional dispersing gas 16 can be suitably introduced though conduit26 to assist fluidization in the lower riser region. In FIG. 1, conduit26 is shown connected to a single distribution ring 17 surroundingconduit 5 and having multiple nozzles 18. Other means known in the art,such as a perforated plate, can be used for distributing the additionaldispersing gas 16. Although FIG. 1 shows an embodiment with only asingle injection nozzle assembly 100, other arrangements, such asmultiple feed assemblies 100 in a riser reactor, with each feed assembly100 emitting at least one conical formed spray from outlet passage 11,can be used to achieve the same objective for large FCCUs with higherhydrocarbon feed rates. The number of feed nozzle assemblies 100 in asingle riser can be any reasonable number, but is preferred to be in therange of one to six.

FIGS. 2A, 2B and 2C show details of the caps 32 and 48 which terminateconduits. 22 and 38 respectively at the end of feed injection assembly100 in the preferred embodiment of FIG. 1. FIG. 2A is a cross-sectionalview, taken along the line 2A—2A of FIG. 1, of the conduits 22, 38 withtheir respective caps 32, 48 and conduit 5 with protection material 7.The first dispersing gas 12 passes through conduit 22 to first cap 32and exits at dispersing gas outlet passages 14 into the mixing zone 42which is in the vicinity of the discharge of outlet passage 14, betweencaps 32 and 48, and upstream of circular slot outlet discharge 11. Theoutlet passage 14 is shown to be on conical surface 35 of cap 32 suchthat the first dispersion gas 12 is discharged through passage 14 in agenerally radial outward and, preferably upward, direction and mixed ina cross-flow with liquid hydrocarbon feed in the mixing zone 42. Theupward discharge angle of passage 14 is more preferably in a range of10° to 90° from the axis of nozzle assembly 100, and most preferably inthe range of 20° to 80° from the axis of nozzle assembly 100. Theresulting angle 33 of the conical surface of first cap 32 of theembodiments illustrated by the Figures can then suitably be in a rangeof 100° to 170°, and preferably in the range of 110° to 160°. The amountof first dispersing gas 12 can be in the range of 0.2 to 7 weightpercent of the hydrocarbon feed 8, but is preferably in the range of 0.5to 5 weight percent of the hydrocarbon feed 8. The discharge velocity offirst dispersing gas 12 through passage 14 can be in the range of 15.2and 244 m/s (50 to 800 ft/sec), but is preferably in the range of 30.4and 152 m/s (100 to 500 ft/sec). The hydrocarbon feed 8 passes throughconduit 38 via annulus 9 to cap 48 and mixes in a cross-flow with thedispersing gas 12 from passages 14 in the mixing zone 42, resulting inthe formation of a fine two-phase mixture of small steam bubbles in theliquid hydrocarbon just upstream of passage 11 which is substantiallyaligned with the first dispersing gas outlet passage 14. The substantialalignment of passages 14 and 11 assures that the fine two-phase mixtureof small steam bubbles in the liquid hydrocarbon passes through passage11 as soon as the mixture is formed in the mixing zone 42, thusminimizing the tendency of re-coalescence and maximizing energyefficiency of the first dispersing gas for atomization. As the finetwo-phase mixture of small steam bubbles in the liquid hydrocarbonpasses through outlet passages 11 into the riser reactor 1, thetwo-phase mixture suddenly expands, due to the pressure drop throughpassage 11, resulting in the formation of a fine atomization ofhydrocarbon feed 8 with narrow droplet size distribution and evendistribution. The pressure drop through passages 11 can be in the rangeof 0.689 and 6.89 bar (10 to 100 psi), but is preferably in the range of1.38 and 4.8 bar (20 to 70 psi). Outlet passage 11 is shown to have achamfer 41 at the end of the passage 11 to assist the sudden radialexpansion of two-phase flow and the fine atomization of hydrocarbon feed8 into the riser reactor 1. Preferably the chamfer 41 has an anglebetween 0° and 40° and more preferably between 0° and 10° with theoutlet passage 11. Cap 48 and outlet passage 11 can include a protectionlayer 50, such as STELLITE or other material known to those skilled inthe art, to prevent damage by the catalyst. The outlet passage 11 isshown to be on a conical surface 45 of cap 48 such that the mixture offirst dispersion gas 12 and liquid hydrocarbon 8 is discharged throughpassage 11 in generally a radially outward and, preferably upward,direction. As described above for the upward discharge angle of passage14, the corresponding upward discharge angle of passage 11 is alsopreferably in a range of 10° to 90° from the axis of nozzle assembly100, and more preferably in the range of 20° to 80° from the axis ofnozzle assembly 100. The resulting angle 43 of the conical surface 45 ofcap 48 of the embodiments illustrated by the Figures can then suitablybe in a range of 100° to 170°, but is preferably in the range of 110° to160°. Preferably conical surface and 45 are arranged parallel withrespect to each other as shown in this Figure. Although caps 32 and 48are shown to include conical surfaces and 45, respectively, other typesof surfaces, such as spherical or elliptical surfaces, can be includedon caps 32 and 48 as long as passages 14 and 11 can be positioned onthese surfaces so as to discharge the first dispersion steam 12 andhydrocarbon feed 8 in generally a radially outward and, preferablyupward, direction.

FIG. 2B shows a plan view of the second cap 48 located at the end ofhydrocarbon conduit 38. Cap 48 is shown to have a circular slotconsisting of four elongated, curved outlet passages 11 on conicalsurface as an example for emitting a conical formed spray consisting offour individual fan sprays of mixtures of first dispersing gas 12 andhydrocarbon feed 8 in a radially outward and upward direction into theriser 1. The angle of each of the fan sprays, as seen from above,emitted from one single passage 11 can be in the range of 30° to 120°,preferably in the range of 60° to 100°.

FIG. 2C shows a plan view of the first cap 32 located at the end of thefirst dispersing gas conduit 22. Cap 32 is shown as having four groupsof circular outlet passages 14 on conical surface arranged in fourcurved lines behind, and substantially aligned with, passages 11 of FIG.2B. Although each group of dispersing gas outlet passages 14 is shown toconsist of six substantially round passages for each individual fanspray emitted from passages 11, the number of passages 14 in each groupcould be any reasonable number. The total number of passages 14 presenton cap 32 will depend on the size of the feed nozzle assembly and cansuitably vary between 40 and 300.

FIG. 5A shows a plan view of the second cap 48 located at the end ofhydrocarbon conduit 38 as in FIG. 2B. It has been found advantageousthat the annular outlet passage 11 is open along its entirecircumferential as illustrated in FIG. 5A. In FIG. 2B the circular slotis divided by four bridges resulting in four separate passageways 11. Byreducing or omitting the bridges, of FIG. 2B, one single circular slotopening and one single conical formed spray results. This isadvantageous to achieve a more uniform and unobstructed flow of themixture of first dispersing gas 12 and hydrocarbon feed 8 into riser 1.Optionally, but less preferred, a plurality of concentric slots can beused as passageways 11.

Preferably the gas outlet passages 14 in first cap 32 are arranged inone circular line behind and substantially aligned with passage 11 asshown in FIG. 5B. Preferably outlet passages 14 constitute one singlegroup as shown in FIG. 5B, in contrast with the different groups ofoutlet passages as shown in FIG. 2C. This one group of outlet passages14 may be arranged along one or more concentric lines on first cap 32.FIG. 5B illustrates two concentric lines of passageways 14.

FIG. 6 shows a nozzle assembly 100 provided with a passageway 55 forenabling part of the liquid hydrocarbon feed material to be dischargedin a more central position, between the first cap 32 and second cap 48,than the position of the outlet passageways 14 of said first cap 32. Insuch a preferred design liquid hydrocarbon feed material will flow fromat least two directions to the mixing zone 42 present betweenpassageways 11 and 14. One direction is a flow from a central region 56between caps 32 and 48 and the other direction is a flow directly fromannulus 9. It has been found that by introducing the hydrocarbon feedmaterial to the mixing zone 42 in this manner an even more uniformmixing of first dispersing gas and hydrocarbon feed results. In a mostpreferred embodiment a substantially equal flow of hydrocarbons flowfrom either side to mixing zone 42 exists. In some practical embodimentsthis volume flow ratio of central and annular flow may suitably varybetween 1 and 5. The hydrocarbon feed material supplied to the centralregion 56 can be fed via a separate supply conduit present in conduit22, wherein this hydrocarbon feed rate can be suitably externallycontrolled.

Preferably part of the hydrocarbon feed material is fed to the centralregion 56 as shown in FIG. 6. FIG. 6 shows an embodiment wherein one ormore conduits 55 fluidly connect the central region 56 between secondcap 48 and first cap 32 via inlet opening 58 with the lower part ofannulus 9. The outlet openings 57 of conduits 55 are more centrallylocated than the mixing zone 42 and the passageways 14 on said first cap32. Preferably the ratio of the total cross sectional area of allconduits 55 and the smallest area of the annulus 9 is between 1:1 and1:5. The number of conduits 55 can be between 1 and 15. A too largenumber will not be beneficial to the mechanical strength of the nozzle.A too low number will not achieve the desired mixing effect. A preferrednumber of passageways 55 is from 4 to and including 8.

The second cap 48 can be fixed onto the nozzle 100 by means of one ormore fixing means 59, for example by means of a bolt or welded pin,connecting the second cap with the first cap 32.

FIG. 7 shows a first cap 32 of FIG. 6 as seen from above, provided withfive outlet openings 57 and two concentric lines of passageways 14 andfixing means 59.

The major improvement of the present invention over the prior art bottomentry nozzles, such as disclosed in U.S. Pat. No. 4,795,547, is muchbetter feed atomization and riser reliability. In the prior art of U.S.Pat. No. 4,795,547, shown in FIG. 3, the hydrocarbon enters throughconduit 5 and single phase atomization nozzle 11 and dispersing gasenters through conduit 4 and annulus 6. Feed atomization occurs as thefeed exits single phase atomization nozzle 11, far upstream from theexit into the riser 2. The feed from nozzle 11 and the dispersing gas inannulus 6 are both moving in a substantially axial direction with verylittle cross-flow mixing between the two. The atomized feed droplets arethen conveyed in substantially longitudinal flow, by the dispersing gasentering through conduit 4, and impinge on the exit deflection cone 13which suddenly alters the direction of the feed droplets fromsubstantially longitudinal flow to radially outward and upward.

The improvements of the present invention over the prior art of U.S.Pat. No. 4,795,547 includes:

Two phase atomization vs. single phase atomization: In U.S. Pat. No.4,795,547, feed atomization occurs mostly through a single-phaseatomization nozzle 11 as shown in FIG. 3 which is far less efficientcompared to the present invention using a two-fluid atomizer throughcaps 32 and 48 in FIG. 1.

Atomization at the exit vs. upstream atomization: In U.S. Pat. No.4,795,547, feed atomization occurs mostly through a single-phaseatomization nozzle 11 shown in FIG. 3 far upstream of the final exit. Asthe atomized feed droplets are conveyed by the dispersing gas, dropletscan coalesce on the surface of the conveying conduit leading to pooratomization. In the present invention, feed atomization occurs at thevery exit by aligning first dispersing gas outlet passage 14 withpassage 11, forming a fine two-phase mixture of small steam bubbles inthe liquid hydrocarbon by cross-flow mixing in mixing zone 42 betweencaps 32 and 48 just upstream of passage 11, and passing the two-phasemixture through outlet passages 11 for fine atomization. There is noconveying conduit with atomized droplets which could lead tore-coalescence.

Direct discharge vs. diverter cone: In U.S. Pat. No. 4,795,547, adiverter cone at the exit is used to suddenly alter the direction of thefeed droplets from substantially longitudinal flow to radially outwardand upward. This leads to impingement of droplets on the cone surfaceand significant worsening of atomization. In the present invention, feedatomization occurs at the exit of caps 32 and 48 which direct the firstdispersing gas 12 and the mixture of the first dispersing gas 12 andliquid hydrocarbon feed 8 in substantially radial directions throughpassages 14 and 11. There is no diverter cone or sudden direction changeof atomized feed which could lead to re-coalescence.

Because of the improvement in feed atomization by the present inventionover the prior art bottom entry nozzles, such as of U.S. Pat. No.4,795,547, the jet penetration of hydrocarbon feed emitted in a radiallyoutward direction into the riser is shorter with the present invention.This prevents the riser damage caused by direct impingement ofhydrocarbon feed which is known to occur with the prior art bottom entrynozzles, such as of U.S. Pat. No. 4,795,547, which dischargeshydrocarbon feed in a sheet of liquid.

Atomization of two nozzles, one according to the present invention ofFIGS. 1 and 2 and the other according to the prior art of U.S. Pat. No.4,795,547 patent, shown as FIG. 3 herein, were tested in ambientcondition using air to simulate the dispersing gas and water to simulatethe hydrocarbon feed. Test results confirm that the nozzle of thepresent invention has much better atomization, compared to the prior artof U.S. Pat. No. 4,795,547 patent. The average droplet size generated bythe nozzle of the present invention was about ⅓ of the prior art designof U.S. Pat. No. 4,795,547 patent under the same operating conditions.Test results also confirm that the nozzle of the present invention hasshorter jet penetration, compared to the prior art of U.S. Pat. No.4,795,547 patent.

The major improvements of the present invention over the prior art ofside entry nozzles, such as U.S. Pat. No. 5,794,857 to Chen et al., arethat adequate feed atomization can be achieved by the present inventionof the improved bottom entry nozzle, thus overcoming the need for using;side entry nozzles and the associated drawbacks of lower riser volume,higher catalyst deactivation and lower, catalyst circulation. The costof installing the improved bottom entry nozzle of the present inventionis also much lower compared to typical side entry nozzles. Furthermore,a better feed distribution across the riser reactor can be achieved withthe present invention when compared to typical multiple side entrynozzles of prior art. This is demonstrated by FIG. 4A which shows a planview of typical prior art feed distribution in a cross section of theriser using four side entry nozzles of prior art, such as U.S. Pat. No.5,794,857, spaced 90° apart, emitting four fan jets radially inward,having an angle of 95° from each fan spray. FIG. 4A shows thatsubstantial areas, shown as the double-shaded areas 44, are covered byoverlapping spray patterns from adjacent nozzles. It also shows thatsubstantial areas, shown as blank areas 46, are not covered at all byany of the four fan sprays. The combination of these two features leadsto undesirable results of uneven feed distribution by the prior art oftypical side entry nozzles where some areas in the riser have no feedcoverage at all and some areas have too much feed. FIG. 4B shows thefeed distribution patterns in a cross-section of the riser reactor for asingle bottom entry feed nozzle emitting four fan sprays radiallyoutward, spaced 90° apart, according to the embodiment of FIGS. 1 and 2with four outlet passages 11. Each fan spray emitted from the passages11 has an angle of 95°. It is shown that, with exactly the same numberof jets and the same spray angle as the prior art side entry nozzles,but changing the feed injection from radially inward in FIG. 4A toradially outward in FIG. 4B, most of the riser reactor area is evenlycovered by the present invention and there is no overlapping of adjacentfan sprays. This clearly demonstrates that the present invention hassuperior feed distribution when compared to the typical feeddistribution of prior art side entry nozzles, such as U.S. Pat. No.5,794,857 to Chen et al.

EXAMPLE

A single bottom entry nozzle according to the present invention of FIG.1 was installed in one of Assignee's FCC units which originally had asingle bottom entry nozzle according to the prior art, shown in FIG. 2of U.S. Pat. No. 4,795,547 patent, reproduced as FIG. 3 herein.

Operating conditions of the FCCU, before and after the revamp, arelisted in Table 1:

TABLE 1 Average Average Post Pre PROCESS CONDITIONS Revamp Revamp DeltaFeed Rate ton/day 5281.3 5185.8 95.5 Feed Temperature ton/day 268.7260.3 8.4 First dispersion Steam ton/day 80.0 36.9 44.1 Seconddispersion Steam ton/day 11.5 11.5 0 Additional dispersing Steam ton/day24.2 18.6 5.6 Reactor Temperature ° C. 494.2 493.2 1.1 Regen Temperature° C. 700.9 697.2 3.8 Liftpot Pressure barg 2.0 2.2 −0.2 Reactor Pressurebarg 1.8 1.9 −0.2 Regen Pressure barg 2.0 2.2 −0.2 Cat Circulation Rateton/min 17.7 17.9 −0.2

The performance of the FCCU, before and after the revamp, are listed inTable 2:

TABLE 2 Average Post Average Pre Revamp Delta Revamp Wt. % of Feed C2-base case −0.2 LPG base case −1.1 Gasoline base case 1.1 Light cycle oilbase case 1.2 Heavy cycle oil & slurry base case −1.3 Coke base case 0.0

The data show that the present invention improves the FCCU performanceby reducing the low value products of C2- dry gas, LPG and thecombination of heavy cycle oil and slurry by 0.2, 1.1 and 1.3 weight %,respectively, and increasing high value products of gasoline and lightcycle oil by 1.1 and 1.2 weight %, respectively. In addition to thebenefit of producing more valuable products, the FCCU also processed1.9% more feed, as shown in the previous table of operating conditions.

What is claimed is:
 1. A nozzle for use in a fluid catalytic crackingunit comprising: a first conduit for providing a passageway for enablinga first dispersing gas to flow therethrough; a first cap covering theend of said first conduit, said first cap including at least one outletpassageway therethrough adapted for discharging said first dispersinggas into a liquid hydrocarbon feed material; a second conduit enclosingsaid first conduit and spaced therefrom to form an annulus therebetweenthereby providing a passageway for enabling said liquid hydrocarbon feedmaterial to flow therethrough; a second cap covering the end of saidsecond conduit, said second cap being spaced from said first cap therebyforming a mixing zone therebetween for mixing said liquid hydrocarbonfeed and said first dispersing gas and said second cap including atleast one continuous circular slot as outlet passageway therethrough,which passageway is substantially aligned with the outlet passageway onsaid first cap and is adapted for discharging said mixture of saidliquid hydrocarbon feed and said first dispersing gas; and said firstcap including at least one attachment to said second cap inside saidcontinuous circular slot.
 2. The nozzle of claim 1, wherein saidcontinuous circular slot includes a chamfer.
 3. The nozzle of claim 2,wherein said chamfer has an angle between 0° and 10° with the outletpassageway.
 4. The nozzle of claim 1 wherein said outlet passagewaythrough said second cap is adapted to discharge said mixture of saidliquid hydrocarbon feed and said first dispersing gas in a generallyradial outward and upward direction.
 5. The nozzle of claim 4, whereinsaid upward discharge angle is in the range of about 20° to 80° from theaxis of said nozzle.
 6. The nozzle of claim 1 wherein said outletpassageway on said first cap includes a plurality of outlet passagewaysfor discharging said first dispersing gas into said liquid hydrocarbonfeed material to form a mixture thereof, and said continuous circularslot outlet passageway on said second cap is open along its entirecircumference, adapted for discharging said mixture of said liquidhydrocarbon feed and said first dispersing gas in a generally radialoutward and upward direction.
 7. The nozzle of claim 1 wherein saidsecond cap includes a conical surface which includes said continuouscircular slot outlet passageway and said first cap includes a conicalsurface having at least one outlet passageway.
 8. The nozzle of claim 1wherein said outlet passageway through said first cap includes aplurality of substantially round holes.
 9. The nozzle of claim 1 whereina passageway is present for enabling part of the liquid hydrocarbon feedmaterial to be discharged in a more central position, between said firstcap and said second cap, relative to the position of said outletpassageway of said first cap.
 10. A fluid catalytic cracking unitcomprising: at least one riser reactor; at least one nozzle located inthe bottom of said riser, wherein said nozzle comprises: a first conduitfor providing a passageway for enabling a first dispersing gas to flowtherethrough; a first cap covering the end of said first conduit, saidfirst cap including at least one outlet passageway therethrough adaptedfor discharging said first dispersing gas into a liquid hydrocarbon feedmaterial; a second conduit enclosing said first conduit and spacedtherefrom to form an annulus therebetween thereby providing a passagewayfor enabling said liquid hydrocarbon feed material to flow therethrough;a second cap covering the end of said second conduit, said second capbeing spaced from said first cap thereby forming a mixing zonetherebetween for mixing said liquid hydrocarbon feed and said firstdispersing gas and said second cap including at least one continuouscircular slot as an outlet passageway therethrough, which passageway issubstantially aligned with said outlet passageway on said first cap andis adapted for discharging said mixture of said liquid hydrocarbon feedand said first dispersing gas; and a regenerator standpipe through whichhot regenerated catalyst enters the riser bottom region.
 11. The fluidcatalytic cracking unit of claim 10 including a third conduitsurrounding said second conduit and forming an annulus therebetween forproviding a passageway for enabling a second dispersing gas to flowtherethrough.
 12. The fluid catalytic cracking unit of claim 11 whereinsaid third conduit of said feed nozzle terminates at a point above thelevel of the centerline of said standpipe entering the riser.
 13. Amethod of injecting feed into a fluid catalytic cracking unit comprisingthe steps of: introducing a liquid hydrocarbon feed and a dispersing gasinto a feed nozzle located in the bottom of a riser, said feed nozzlecomprising: a first conduit for providing a passageway for enabling afirst dispersing gas to flow therethrough; a first cap covering the endof said first conduit, said first cap including at least one outletpassageway therethrough adapted for discharging said first dispersinggas into a liquid hydrocarbon feed material; a second conduit enclosingsaid first conduit and spaced therefrom to form an annulus therebetweenthereby providing a passageway for enabling said liquid hydrocarbon feedmaterial to flow therethrough; a second cap covering the end of saidsecond conduit, said second cap being spaced from said first cap therebyforming a mixing zone therebetween for mixing said liquid hydrocarbonfeed and said first dispersing gas and said second cap including atleast one circular slot as outlet passageway therethrough, whichpassageway is substantially aligned with the outlet passageway on saidfirst cap and is adapted for discharging said mixture of said liquidhydrocarbon feed and said first dispersing gas; and a third conduitsurrounding said second conduit and forming an annulus therebetween forproviding a passageway for enabling a second dispersing gas to flowtherethrough; mixing said liquid hydrocarbon feed and said dispersinggas in a mixing zone in said feed injection system; and discharging saidmixture of said liquid hydrocarbon feed and said dispersing gas fromsaid feed injection system as a conical formed spray in a generallyradial outward and upward direction.